The goal of this project is to study the biomechanical characteristics knees which have undergone reconstructions of the PCL without and with reconstructions of the posterolateral comer. The results will provide important information to the surgeon in terms of selecting a reconstruction technique, graft configurations, and graft pretensioning protocols. Tests with simulated muscle forces will help to formulate guidelines for rehabilitation activities for patients undergoing PCL graft reconstruction. Specific Aim 1: We will study the effects of a new, more anatomic double bundle PCL graft reconstruction upon AP laxities, graft forces and knee kinematics during a series of tibial loading tests. Tests will first be performed on intact knees, and then repeated with double bundle grafts using specific pretensioning protocols. Two PM bundle pre-tensions and two tunnel placement locations will be studied. No associated collateral injuries will be present for these tests. Specific Aim 2: We will determine the optimum isometric locations for placing the femoral tunnels of LCL, POP, and PFL graft reconstructions. Suture isometry measurements will be performed to determine the optimum isometric point (OIP) for each graft, isometry measurements will be repeated with a graft placed in a femoral tunnel drilled at the OIP and adjacent grid locations. A graft isometry map will be generated and the most isometric tunnel location for each graft will be identified and used for subsequent biomechanical tests with posterolateral comer reconstructions (Specific Aim 3). Mean optimum tunnel locations for all specimens will be computed. Specific Aim 3: We will investigate new tensioning strategies for LCL, POP, and PFL grafts placed in femoral tunnels. The objective will be to restore normal external rotation and varus stability, while producing more equal load-sharing between PCL and posterolateral grafts. These posterolateral studies will be performed in conjunction with single and double bundle PCL graft reconstructions. PCL forces and knee kinematics during tibial loading tests will be measured for knees in the intact state and after PCL graft reconstructions. Tests will be repeated with the posterolateral structures sectioned, and again after posterolateral reconstructions have been performed using specific graft tensioning protocols.